1. Field of the Invention
The present invention relates to internal combustion engines and more particularly to engines using internal combustion to pressurize hydraulic fluid.
2. Description of Related Art
A conventional internal combustion reciprocating engine for generating rotational movement includes a series of pistons pivotably coupled to a crankshaft. Each piston is at least partially surrounded by a stationary cylinder so as to define a combustion chamber between the piston and a head of the cylinder. The combustion of a liquid fuel such as gasoline in the combustion chamber produces hot, pressurized gas which drives the piston away from the cylinder head. The pivotable coupling between the piston and the crankshaft converts the linear movement of the piston through the cylinder into rotation of the crankshaft.
Such engines operate cyclically--that is, each cylinder and piston repeatedly perform a sequence of steps which coincide with the strokes of the piston. One conventional four stroke cycle common in automotive engines includes: (1) an intake stroke, during which the piston moves away from the cylinder head while fuel and air enter the combustion chamber; (2) a compression or return stroke, during which the piston moves back toward the cylinder head to compress the fuel-air mixture in the combustion chamber; (3) a combustion or power stroke, during which the fuel-air mixture in the combustion chamber is ignited, generating hot gas which drives the piston away from the cylinder head; and (4) an exhaust stroke, during which the exhaust gas is exhausted from the combustion chamber as the piston moves back toward the cylinder head.
The flow of fuel and exhaust gas through the combustion chamber is controlled by the piston and by valves positioned near the head of the cylinder. During the intake stroke, the piston moves away from the cylinder head, lowering the pressure in the combustion chamber and inducing fuel and air to enter the combustion chamber through one or more intake valves in the cylinder head. During the exhaust stroke, the piston moves back toward to the cylinder head and tends to push the exhaust gas out of the combustion chamber through an exhaust valve in the cylinder head. The intake and exhaust valves remain closed through the remainder of the cycle.
According to a conventional two-stroke cycle, combustion occurs each time the piston approaches the head of the cylinder. The hot, pressurized gas produced by the combustion of the fuel drives the piston away from the cylinder head. As the piston approaches the end of the power stroke, intake and outlet valves are opened, relieving the exhaust gas pressure in the combustion chamber. Fuel and air flow into the combustion chamber. Meanwhile, the piston begins its return stroke toward the cylinder head, compressing the fuel and air in preparation for combustion.
In a conventional reciprocating engine, a series of pistons are coupled to the same crankshaft. The timing of the strokes of different pistons are staggered so that, while one piston is undergoing its combustion stroke, other pistons are undergoing their intake, compression or exhaust strokes. In a conventional multi-piston engine, the rotational power transmitted to the crankshaft as one piston undergoes its combustion stroke drives other pistons through their intake, compression and exhaust strokes. Likewise, power drawn from the crankshaft opens and closes the intake and exhaust valves.
Conventional reciprocating engines typically include flywheels. The power supplied by the engine to the drive shaft is periodic rather than continuous in the sense that a burst of power is supplied each time a piston is fired. The flywheel tends to smooth out the power supplied by the engine over time to provide a constant torque to the drive shaft.
The efficiency of the engine relates, at least in part, to the duration of the combustion stroke. A longer stroke leads to more complete combustion of the fuel and to more efficient conversion of the gas pressure into mechanical work.
One drawback to conventional internal combustion reciprocating engines is that the duration of the combustion stroke is controlled by the speed at which the crankshaft rotates. In practice, this significantly limits the duration of the combustion stroke. While idling at 500 revolutions per minute (RPM), the combustion stroke of a conventional automotive engine lasts approximately one-sixteenth (1/16) second. At 2000 RPM, the approximate output of a conventional automotive engine of an automobile traveling 60 miles per hour, the combustion stroke of the engine lasts approximately one-sixtieth 1/60) second. This is simply not enough time for the fuel-air mixture to burn completely. At least partially as a result, the efficiency of conventional automotive engines is in the neighborhood of 18%.
Furthermore, the incomplete combustion of the fuel during the combustion stroke of a conventional four stroke cycle engine increases the pollution content of the exhaust. The residual pressure remaining in the exhaust gas when relieved from the cylinder increases the noise of the engine. Therefore, there remains a need in the art for an internal combustion engine capable of a longer power stroke.